Understanding ACLs

ACL Overview

An ACL is a collection of sequential permit and deny conditions that applies to packets. When a packet is received on an interface, the switch compares the fields in the packet against any applied ACLs to verify that the packet has the permissions required to be forwarded, based on the conditions specified in the access lists. It tests the packets against the conditions in an access list one-by-one. The first match determines whether the switch accepts or rejects the packets. Because the switch stops testing conditions after the first match, the order of conditions in the list is critical. If no conditions match, the switch drops the packet. If there are no restrictions, the switch forwards the packet; otherwise, the switch drops the packet.

Switches traditionally operate at Layer 2, switching traffic within a VLAN, whereas routers route traffic between VLANs at Layer 3. The Catalyst 4500 series switch can accelerate packet routing between VLANs by using Layer 3 switching. The Layer 3 switch bridges the packet, and then routed the packet internally without going to an external router. The packet is then bridged again and sent to its destination. During this process, the switch can control all packets, including packets bridged within a VLAN.

You configure access lists on a router or switch to filter traffic and provide basic security for your network. If you do not configure ACLs, all packets passing through the switch could be allowed on all parts of the network. You can use ACLs to control which hosts can access different parts of a network or to decide which types of traffic are forwarded or blocked at router interfaces. For example, you can allow e-mail traffic to be forwarded but not Telnet traffic. ACLs can be configured to block inbound traffic, outbound traffic, or both. However, on Layer 2 interfaces, you can apply ACLs only in the inbound direction.

An ACL contains an ordered list of access control entries (ACEs). Each ACE specifies permit or deny and a set of conditions the packet must satisfy in order to match the ACE. The meaning of permit or deny depends on the context in which the ACL is used.

Supported Features That Use ACLs

The switch supports two applications of ACLs to filter traffic:

•Router ACLs are applied to Layer 3 interfaces. They control the access of routed traffic between VLANs. All Catalyst 4500 series switches can create router ACLs, but you must have a Cisco IOS software image on your switch to apply an ACL to a Layer 3 interface and filter packets routed between VLANs.

•Port ACLs perform access control on traffic entering a Layer 2 interface. If there are not enough hardware CAM entries, the output port ACL is not applied to the port and a warning message is given to user. (This restriction applies to all access group modes for output port ACLs.) When there are enough CAM entries, the output port ACL might be reapplied.

If there is any output port ACL configured on a Layer 2 port, then no VACL or router ACL can be configured on the VLANs that the Layer 2 port belongs to. Also, the reverse is true: port ACLs and VLAN-based ACLs (VACLs and router ACLs) are mutually exclusive on a Layer 2 port. This restriction applies to all access group modes.

You can apply only one IP access list and one MAC access list to a Layer 2 interface.

•VLAN ACLs or VLAN maps control the access of all packets (bridged and routed). You can use VLAN maps to filter traffic between devices in the same VLAN. You do not need the enhanced image to create or apply VLAN maps. VLAN maps are configured to control access based on Layer 3 addresses for IP. MAC addresses using Ethernet ACEs control the access of unsupported protocols. After you apply a VLAN map to a VLAN, all packets (routed or bridged) entering the VLAN are checked against that map. Packets can either enter the VLAN through a switch port or through a routed port after being routed.

You can use both router ACLs and VLAN maps on the same switch.

Router ACLs

You can apply router ACLs on switch virtual interfaces (SVIs), which are Layer 3 interfaces to VLANs; on physical Layer 3 interfaces; and on Layer 3 EtherChannel interfaces. Router ACLs are applied on interfaces for specific directions (inbound or outbound). You can apply one IP access list in each direction.

Multiple features can use one ACL for a given interface, and one feature can use multiple ACLs. When a single router ACL is used by multiple features, it is examined multiple times. The access list type determines the input to the matching operation:

The switch examines ACLs associated with features configured on a given interface and a direction. As packets enter the switch on an interface, ACLs associated with all inbound features configured on that interface are examined. After packets are routed and before they are forwarded to the next hop, all ACLs associated with outbound features configured on the egress interface are examined.

ACLs permit or deny packet forwarding based on how the packet matches the entries in the ACL. For example, you can use access lists to allow one host to access a part of a network, but prevent another host from accessing the same part. In Figure 35-1, ACLs applied at the router input allow Host A to access the Human Resources network, but prevent Host B from accessing the same network.

Figure 35-1 Using ACLs to Control Traffic to a Network

Port ACLs

You can also apply ACLs to Layer 2 interfaces on a switch. Port ACLs are supported on physical interfaces and EtherChannel interfaces.

As with router ACLs, the switch examines ACLs associated with features configured on a given interface and permits or denies packet forwarding based on how the packet matches the entries in the ACL. In the example in Figure 35-1, if all workstations were in the same VLAN, ACLs applied at the Layer 2 input would allow Host A to access the Human Resources network, but prevent Host B from accessing the same network.

When you apply a port ACL to a trunk port, the ACL filters traffic on all VLANs present on the trunk port. When you apply a port ACL to a port with voice VLAN, the ACL filters traffic on both data and voice VLANs.

With port ACLs, you can filter IP traffic by using IP access lists and non-IP traffic by using MAC addresses. You can filter both IP and non-IP traffic on the same Layer 2 interface by applying both an IP access list and a MAC access list to the interface.

Note You cannot apply more than one IP access list and one MAC access list to a Layer 2 interface. If an IP access list or MAC access list is already configured on a Layer 2 interface and you apply a new IP access list or MAC access list to the interface, the new ACL replaces the previously configured one.

VLAN Maps

VLAN maps can control the access of all traffic in a VLAN. You can apply VLAN maps on the switch to all packets that are routed into or out of a VLAN or are bridged within a VLAN. Unlike router ACLs, VLAN maps are not defined by direction (input or output).

You can configure VLAN maps to match Layer 3 addresses for IP traffic. Access of all non-IP protocols is controlled with a MAC address and an Ethertype using MAC ACLs in VLAN maps. (IP trafficis not controlled by MAC ACLs in VLAN maps.) You can enforce VLAN maps only on packets going through the switch; you cannot enforce VLAN maps on traffic between hosts on a hub or on another switch connected to this switch.

With VLAN maps, forwarding packets is permitted or denied, based on the action specified in the map. Figure 35-2 illustrates how a VLAN map is applied to deny a specific type of traffic from Host A in VLAN 10 from being forwarded.

Figure 35-2 Using VLAN Maps to Control Traffic

Hardware and Software ACL Support

This section describes how to determine whether ACLs are processed in hardware or in software:

•Flows that match a deny statement in standard and extended ACLs (input only) are dropped in hardware if ICMP unreachable messages are disabled.

•Flows that match a permit statement in standard and extended ACLs (input and output) are processed in hardware.

•The following ACL types are not supported in software:

–Standard Xerox Network Systems (XNS) Protocol access list

–Extended XNS access list

–DECnet access list

–Protocol type-code access list

–Standard Internet Packet Exchange (IPX) access list

–Extended IPX access list

Note Packets that require logging are processed in software. A copy of the packets is sent to the CPU for logging while the actual packets are forwarded in hardware so that non-logged packet processing is not impacted.

By default, the Catalyst 4500 series switch sends ICMP unreachable messages when a packet is denied by an access list; these packets are not dropped in hardware but are forwarded to the switch so that it can generate the ICMP unreachable message.

To drop access-list denied packets in hardware on the input interface, you must disable ICMP unreachable messages using the no ip unreachables interface configuration command. The ip unreachables command is enabled by default.

Packets denied by an output access list are always forwarded to the CPU.

TCAM Programming and ACLs

Two types of hardware resources are consumed when you program ACLs: entries and masks. If one of these resources is exhausted, no additional ACLs can be programmed into hardware. If the masks on a system are exhausted, but entries are available, changing the programming scheme from packed to scattered might free up masks, allowing additional ACLs to be programmed into hardware.

The goal is to use TCAM resources more efficiently by minimizing the number of masks per ACL entries. To compare TCAM utilization when employing the scattered or packed algorithms, use the show platform hardware acl statistics utilization brief command. To change the algorithm from packed to scattered, use the access-list hardware entries command. To disable an algorithm, use the no acccess-list hardware entries command.

Note To determine whether the packed algorithm is configured, use the show running config command. If packed is configured, the line access-list hardware entries packed will appear.

Note The default TCAM programming algorithm is packed.

The following output was collected from a switch running in packed mode. Observe that 89 percent of the masks are required to program only 49 percent of the ACL entries.

Switch# configure terminal

Enter configuration commands, one per line. End with CNTL/Z.

Switch(config)# access-list hardware entries packed

Switch(config)# end

Switch#

01:15:34: %SYS-5-CONFIG_I: Configured from console by console

Switch#

Switch# show platform hardware acl statistics utilization brief

Entries/Total(%) Masks/Total(%)

----------------- ---------------

Input Acl(PortAndVlan) 2016 / 4096 ( 49) 460 / 512 ( 89)

Input Acl(PortOrVlan) 6 / 4096 ( 0) 4 / 512 ( 0)

Input Qos(PortAndVlan) 0 / 4096 ( 0) 0 / 512 ( 0)

Input Qos(PortOrVlan) 0 / 4096 ( 0) 0 / 512 ( 0)

Output Acl(PortAndVlan) 0 / 4096 ( 0) 0 / 512 ( 0)

Output Acl(PortOrVlan) 0 / 4096 ( 0) 0 / 512 ( 0)

Output Qos(PortAndVlan) 0 / 4096 ( 0) 0 / 512 ( 0)

Output Qos(PortOrVlan) 0 / 4096 ( 0) 0 / 512 ( 0)

L4Ops: used 2 out of 64

The following output was collected after the algorithm was switched to scattered. Observe that the
number of masks required to program 49 percent of the entries has decreased to 49 percent.

Note When you enable DHCP snooping and IP Source Guard on all ports on a chassis, you must use the scattered keyword.

Switch# configure terminal

Enter configuration commands, one per line. End with CNTL/Z.

Switch(config)# access-list hardware entries scattered

Switch(config)# end

Switch#

01:39:37: %SYS-5-CONFIG_I: Configured from console by console

Switch#

Switch# show platform hardware acl statistics utilization brief

Entries/Total(%) Masks/Total(%)

----------------- ---------------

Input Acl(PortAndVlan) 2016 / 4096 ( 49) 252 / 512 ( 49)

Input Acl(PortOrVlan) 6 / 4096 ( 0) 5 / 512 ( 0)

Input Qos(PortAndVlan) 0 / 4096 ( 0) 0 / 512 ( 0)

Input Qos(PortOrVlan) 0 / 4096 ( 0) 0 / 512 ( 0)

Output Acl(PortAndVlan) 0 / 4096 ( 0) 0 / 512 ( 0)

Output Acl(PortOrVlan) 0 / 4096 ( 0) 0 / 512 ( 0)

Output Qos(PortAndVlan) 0 / 4096 ( 0) 0 / 512 ( 0)

Output Qos(PortOrVlan) 0 / 4096 ( 0) 0 / 512 ( 0)

L4Ops: used 2 out of 64

Switch#

Layer 4 Operators in ACLs

The following sections describe guidelines and restrictions for configuring ACLs that include Layer 4 port operations:

Restrictions for Layer 4 Operations

You can specify these operator types, each of which uses one Layer 4 operation in the hardware:

•gt (greater than)

•lt (less than)

•neq (not equal)

•range (inclusive range)

We recommend that you not specify more than six different operations on the same ACL. If you exceed this number, each new operation might cause the affected ACE (access control entry) to be translated into multiple ACEs in hardware. If you exceed this number, the affected ACE might be processed in software.

Configuration Guidelines for Layer 4 Operations

Keep the following guidelines in mind when using Layer 4 operators:

•Layer 4 operations are considered different if the operator or operand differ. For example, the following ACL contains three different Layer 4 operations because gt 10 and gt 11 are considered two different Layer 4 operations:

... gt 10 permit

... lt 9 deny

... gt 11 deny

Note The eq operator can be used an unlimited number of times because eq does not use a Layer 4 operation in hardware.

•Layer 4 operations are considered different if the same operator/operand couple applies once to a source port and once to a destination port, as in the following example:

... Src gt 10....

... Dst gt 10

A more detailed example follows:

access-list 101

... (dst port) gt 10 permit

... (dst port) lt 9 deny

... (dst port) gt 11 deny

... (dst port) neq 6 permit

... (src port) neq 6 deny

... (dst port) gt 10 deny

access-list 102

... (dst port) gt 20 deny

... (src port) lt 9 deny

... (src port) range 11 13 deny

... (dst port) neq 6 permit

Access lists 101 and 102 use the following Layer 4 operations:

•Access list 101 Layer 4 operations: 5

–gt 10 permit and gt 10 deny both use the same operation because they are identical and both operate on the destination port.

•Access list 102 Layer 4 operations: 4

•Total Layer 4 operations: 8 (due to sharing between the two access lists)

–neg6 permit is shared between the two ACLs because they are identical and both operate on the same destination port.

•A description of the Layer 4 operations usage is as follows:

–Layer 4 operation 1 stores gt 10 permit and gt 10 deny from ACL 101

–Layer 4 operation 2 stores lt 9 deny from ACL 101

–Layer 4 operation 3 stores gt 11 deny from ACL 101

–Layer 4 operation 4 stores neg 6 permit from ACL 101 and 102

–Layer 4 operation 5 stores neg 6 deny from ACL 101

–Layer 4 operation 6 stores gt 20 deny from ACL 102

–Layer 4 operation 7 stores lt 9 deny from ACL 102

–Layer 4 operation 8 stores range 11 13 deny from ACL 102

How ACL Processing Impacts CPU

ACL processing can impact the CPU in two ways:

•For some packets, when the hardware runs out of resources, the software must perform the ACL matches:

–TCP flag combinations other than rst ack and syn fin rst are processed in software. rst ack is equivalent to the keyword established.

–You can specify up to six Layer 4 operations (lt, gt, neq, and range) in an ACL in order for all operations to be guaranteed to be processed in hardware. More than six Layer 4 operations will trigger an attempt to translate the excess operations into multiple ACEs in hardware. If this attempt fails, packets will be processed in software. The translation process is less likely to succeed on large ACLs with a great number of Layer 4 operations, and on switches with large numbers of ACLs configured. The precise limit depends on how many other ACLs are configured and which specific Layer 4 operations are used by the ACLs being translated. The eq operator does not require any Layer 4 operations and can be used any number of times.

–If the total number of Layer 4 operations in an ACL is less than six, you can distribute the operations in any way you choose.

Examples:

The following access lists will be processed completely in hardware:

access-list 104 permit tcp any any established

access-list 105 permit tcp any any rst ack

access-list 107 permit tcp any synfin rst

Access lists 104 and 105 are identical; established is shorthand for rst and ack.

Access list 101, below, will be processed completely in software:

access-list 101 permit tcp any any urg

Because four source and two destination operations exist, access list 106, below, will be processed in hardware:

access-list 106 permit tcp any range 100 120 any range 120 140

access-list 106 permit tcp any range 140 160 any range 180 200

access-list 106 permit tcp any range 200 220

access-list 106 deny tcp any range 220 240

In the following code, the Layer 4 operations for the third ACE will trigger an attempt to translate dst lt 1023 into multiple ACEs in hardware, because three source and three destination operations exist. If the translation attempt fails, the third ACE will be processed in software.

access-list 102 permit tcp any lt 80 any gt 100

access-list 102 permit tcp any range 100 120 any range 120 1024

access-list 102 permit tcp any gt 1024 any lt 1023

Similarly, for access list 103, below, the third ACE will trigger an attempt to translate dst gt 1023 into multiple ACEs in hardware. If the attempt fails, the third ACE will be processed in software. Although the operations for source and destination ports look similar, they are considered different Layer 4 operations.)

access-list 103 permit tcp any lt 80 any lt 80

access-list 103 permit tcp any range 100 120 any range 100 120

access-list 103 permit tcp any gt 1024 any gt 1023

Note Remember that source port lt 80 and destination port lt 80 are considered different operations.

•Some packets must be sent to the CPU for accounting purposes, but the action is still performed by the hardware. For example, if a packet must be logged, a copy is sent to the CPU for logging, but the forwarding (or dropping) is performed in the hardware. Although logging slows the CPU, it does not affect the forwarding rate. This sequence of events would happen under the following conditions:

–When a log keyword is used

–When an output ACL denies a packet

–When an input ACL denies a packet, and on the interface where the ACL is applied, ip unreachableis enabled (ip unreachable is enabled by default on all the interfaces)

Configuring Unicast MAC Address Filtering

To block all unicast traffic to or from a MAC address in a specified VLAN, perform this task:

Command

Purpose

Switch(config)# mac-address-table staticmac_addressvlanvlan_IDdrop

Blocks all traffic to or from the configured unicast MAC address in the specified VLAN.

To clear MAC address-based blocking, use the no form of this command without the drop keyword.

This example shows how to block all unicast traffic to or from MAC address 0050.3e8d.6400 in VLAN 12:

Router# configure terminal

Router(config)# mac-address-table static0050.3e8d.6400vlan12 drop

Configuring Named MAC Extended ACLs

You can filter non-IP traffic on a VLAN and on a physical Layer 2 port by using MAC addresses and named MAC extended ACLs. The procedure is similar to that of configuring other extended named ACLs. You can use a number to name the access list, but MAC access list numbers from 700 to 799 are not supported.

Note Named MAC extended ACLs cannot be applied to Layer 3 interfaces.

For more information about the supported non-IP protocols in the mac access-list extended command, refer to the Catalyst 4500 Series Switch Cisco IOS Command Reference.

Configuring VLAN Maps

This section describes how to configure VLAN maps, which is the only way to control filtering within a VLAN. VLAN maps have no direction. To filter traffic in a specific direction by using a VLAN map, you need to include an ACL with specific source or destination addresses. If there is a match clause for that type of packet (IP or MAC) in the VLAN map, the default action is to drop the packet if the packet does not match any of the entries within the map. If there is no match clause for that type of packet, the default is to forward the packet.

To create a VLAN map and apply it to one or more VLANs, perform this task

Step 1 Create the standard or extended IP ACLs or named MAC extended ACLs that you want to apply to the VLAN.

Step 3 In access map configuration mode, you have the optional to enter an action (forward [the default] or drop) and enter the match command to specify an IP packet or a non-IP packet and to match the packet against one or more ACLs (standard or extended). If a match clause is not specified, the action is applied to all packets. The match clause can be used to match against multiple ACLs. If a packet matches any of the specified ACLs, the action is applied.

Note If the VLAN map has a match clause for the type of packet (IP or MAC) and the packet does not match the type, the default is to drop the packet. If there is no match clause in the VLAN map for that type of packet, and no action specified, the packet is forwarded.

Step 4 Use the vlan filter global configuration command to apply a VLAN map to one or more VLANs.

Note You cannot apply a VLAN map to a VLAN on a switch that has ACLs applied to Layer 2 interfaces (port ACLs).

VLAN Map Configuration Guidelines

Keep the following guidelines in mind when configuring VLAN maps:

•VLAN maps do not filter IPv4 ARP packets.

•If there is no router ACL configured to deny traffic on a routed VLAN interface (input or output), and no VLAN map configured, all traffic is permitted.

•Each VLAN map consists of a series of entries. The order of entries in a VLAN map is important. A packet that comes into the switch is tested against the first entry in the VLAN map. If it matches, the action specified for that part of the VLAN map is taken. If there is no match, the packet is tested against the next entry in the map.

•If the VLAN map has at least one match clause for the type of packet (IP or MAC) and the packet does not match any of these match clauses, the default is to drop the packet. If there is no match clause for that type of packet in the VLAN map, the default is to forward the packet.

•The system might take longer to boot if you have configured a very large number of ACLs.

Creating and Deleting VLAN Maps

Each VLAN map consists of an ordered series of entries. To create, add to, or delete a VLAN map entry, perform this task:

Command

Purpose

Step 1

Switch# configure terminal

Enters global configuration mode.

Step 2

Switch(config)# vlan access-map
name [number]

Creates a VLAN map, and give it a name and (optionally) a number. The number is the sequence number of the entry within the map.

When you create VLAN maps with the same name, numbers are assigned sequentially in increments of 10. When modifying or deleting maps, you can enter the number of the map entry that you want to modify or delete.

This command enables access-map configuration mode.

Step 3

Switch(config-access-map)# action{drop|forward}

(Optional) Sets the action for the map entry. The default is to forward.

Matches the packet (using either the IP or MAC address) against one or more standard or extended access lists. Note that packets are matched only against access lists of the correct protocol type. IP packets are compared with standard or extended IP access lists. Non-IP packets are only compared with named MAC extended access lists. If a match clause is not specified, the action is taken on all packets.

Step 5

Switch(config-access-map)# end

Returns to global configuration mode.

Step 6

Switch(config)#show
running-config

Displays the access list configuration.

Step 7

Switch(config)# copy
running-config startup-config

(Optional) Saves your entries in the configuration file.

You can use the no vlan access-mapname global configuration command to delete a map. You can use the no vlan access-mapnamenumber global configuration command to delete a single sequence entry from within the map. You can use the no action access-map configuration command to enforce the default action, which is to forward.

VLAN maps do not use the specific permit or deny keywords. To deny a packet by using VLAN maps, create an ACL that would match the packet, and then set the action to drop. A permit in the ACL is the same as a match. A deny in the ACL means no match.

Examples of ACLs and VLAN Maps

These examples show how to create ACLs and VLAN maps that for specific purposes.

Example 1

This example shows how to create an ACL and a VLAN map to deny a packet. In the first map, any packets that match theip1ACL (TCP packets) would be dropped. You first create the ip1 ACL to permit any TCP packet and no other packets. Because there is a match clause for IP packets in the VLAN map, the default action is to drop any IP packet that does not match any of the match clauses.

Switch(config)# ip access-list extended ip1

Switch(config-ext-nacl)# permit tcp any any

Switch(config-ext-nacl)# exit

Switch(config)# vlan access-map map_1 10

Switch(config-access-map)# match ip address ip1

Switch(config-access-map)# action drop

This example shows how to create a VLAN map to permit a packet. ACL ip2 permits UDP packets; and any packets that match the ip2 ACL are forwarded.

Switch(config)# ip access-list extended ip2

Switch(config-ext-nacl)# permit udp any any

Switch(config-ext-nacl)# exit

Switch(config)# vlan access-map map_1 20

Switch(config-access-map)# match ip address ip2

Switch(config-access-map)# action forward

In this map, any IP packets that did not match any of the previous ACLs (that is, packets that are not TCP packets or UDP packets) would get dropped.

Example 2

In this example, the VLAN map is configured to drop IP packets and to forward MAC packets by default. By applying standard ACL 101 and the extended named access lists igmp-match and tcp-match, the VLAN map is configured to do the following:

•Forward all UDP packets

•Drop all IGMP packets

•Forward all TCP packets

•Drop all other IP packets

•Forward all non-IP packets

Switch(config)# access-list 101 permit udp any any

Switch(config)# ip access-list extended igmp-match

Switch(config-ext-nacl)# permit igmp any any

Switch(config)# ip access-list extended tcp-match

Switch(config-ext-nacl)# permit tcp any any

Switch(config-ext-nacl)# exit

Switch(config)# vlan access-map drop-ip-default 10

Switch(config-access-map)# match ip address 101

Switch(config-access-map)# action forward

Switch(config-access-map)# exit

Switch(config)# vlan access-map drop-ip-default 20

Switch(config-access-map)# match ip address igmp-match

Switch(config-access-map)# action drop

Switch(config-access-map)# exit

Switch(config)# vlan access-map drop-ip-default 30

Switch(config-access-map)# match ip address tcp-match

Switch(config-access-map)# action forward

Example 3

In this example, the VLAN map is configured to drop MAC packets and forward IP packets by default. By applying MAC extended access lists, good-hosts and good-protocols, the VLAN map is configured to do the following:

Example 4

In this example, the VLAN map is configured to drop all packets (IP and non-IP). By applying access lists tcp-match and good-hosts, the VLAN map is configured to do the following:

•Forward all TCP packets

•Forward MAC packets from hosts 0000.0c00.0111 and 0000.0c00.0211

•Drop all other IP packets

•Drop all other MAC packets

Switch(config)# vlan access-map drop-all-default 10

Switch(config-access-map)# match ip address tcp-match

Switch(config-access-map)# action forward

Switch(config-access-map)# exit

Switch(config)# vlan access-map drop-all-default 20

Switch(config-access-map)# match mac address good-hosts

Switch(config-access-map)# action forward

Applying a VLAN Map to a VLAN

To apply a VLAN map to one or more VLANs, perform this task:

Command

Purpose

Step 1

Switch# configure terminal

Enters global configuration mode.

Step 2

Switch(config)# vlan filtermapnamevlan-listlist

Applies the VLAN map to one or more VLAN IDs.

The list can be a single VLAN ID (22), a consecutive list (10-22), or a string of VLAN IDs (12, 22, 30). Spaces around comma, and dash, are optional.

Step 3

Switch(config)#show
running-config

Displays the access list configuration.

Step 4

cSwitch(config)# copy
running-config startup-config

(Optional) Saves your entries in the configuration file.

Note You cannot apply a VLAN map to a VLAN on a switch that has ACLs applied to Layer 2 interfaces (port ACLs).

This example shows how to apply VLAN map 1 to VLANs 20 through 22:

Switch(config)# vlan filter map 1 vlan-list 20-22

Using VLAN Maps in Your Network

Figure 35-3 shows a typical wiring closet configuration. Host X and Host Y are in different VLANs, connected to wiring closet switches A and C. Traffic moving from Host X to Host Y is routed by Switch B. Access to traffic moving from Host X to Host Y can be controlled at the entry point of Switch A. In the following configuration, the switch can support a VLAN map and a QoS classification ACL.

Figure 35-3 Wiring Closet Configuration

For example, if you do not want HTTP traffic to be switched from Host X to Host Y, you could apply a VLAN map on Switch A to drop all HTTP traffic moving from Host X (IP address 10.1.1.32) to Host Y (IP address 10.1.1.34) at Switch A and not bridge the traffic to Switch B. To configure this scenario, you would do the following:

First, define an IP access list http to permit (match) any TCP traffic on the HTTP port, as follows:

Next, create a VLAN access map named map2 so that traffic that matches the http access list is dropped and all other IP traffic is forwarded, as follows:

Switch(config)# vlan access-map map2 10

Switch(config-access-map)# match ip address http

Switch(config-access-map)# action drop

Switch(config-access-map)# exit

Switch(config)# ip access-list extended match_all

Switch(config-ext-nacl)# permit ip any any

Switch(config-ext-nacl)# exit

Switch(config)# vlan access-map map2 20

Switch(config-access-map)# match ip address match_all

Switch(config-access-map)# action forward

Then, apply the VLAN access map named map2 to VLAN 1, as follows:

Switch(config)# vlan filter map2 vlan 1

Denying Access to a Server on Another VLAN

Figure 35-4 shows how to restrict access to a server on another VLAN. In this example, server 10.1.1.100 in VLAN 10 has the following access restrictions:

•Hosts in subnet 10.1.2.0/8 in VLAN 20 should not have access.

•Hosts 10.1.1.4 and 10.1.1.8 in VLAN 10 should not have access.

Figure 35-4 Deny Access to a Server on Another VLAN

This procedure configures ACLs with VLAN maps to deny access to a server on another VLAN. The VLAN map SERVER 1_ACL denies access to hosts in subnet 10.1.2.0/8, host 10.1.1.4, and host 10.1.1.8. Then it permits all other IP traffic. In Step 3, VLAN map SERVER1 is applied to VLAN 10.

Step 2 Define a VLAN map using the ACL to drop IP packets that match SERVER1_ACL and forward IP packets that do not match the ACL.

Switch(config)# vlan access-map SERVER1_MAP

Switch(config-access-map)# match ip address SERVER1_ACL

Switch(config-access-map)# action drop

Switch(config)# vlan access-map SERVER1_MAP 20

Switch(config-access-map)# action forward

Switch(config-access-map)# exit

Step 3 Apply the VLAN map to VLAN 10.

Switch(config)# vlan filter SERVER1_MAP vlan-list 10.

Displaying VLAN Access Map Information

To display information about VLAN access maps or VLAN filters, perform one of these tasks.

Command

Purpose

Switch# show vlan access-map [mapname]

Show information about all VLAN access-maps or the specified access map.

Switch# show vlan filter [access-map name |
vlan vlan-id]

Show information about all VLAN filters or about a specified VLAN or VLAN access map.

This is a sample output of the show vlan access-map command:

Switch# show vlan access-map

Vlan access-map "map_1" 10

Match clauses:

ip address: ip1

Action:

drop

Vlan access-map "map_1" 20

Match clauses:

mac address: mac1

Action:

forward

Vlan access-map "map_1" 30

Match clauses:

Action:

drop

Note Sequence 30 does not have a match clause. All packets (IP as well as non-IP) will be matched against it and dropped.

This is a sample output of the show vlan filter command:

Switch# showvlanfilter

VLAN Map map_1 is filtering VLANs:

20-22

Using VLAN Maps with Router ACLs

If the VLAN map has a match clause for a packet type (IP or MAC) and the packet does not match the type, the default is to drop the packet. If there is no match clause in the VLAN map, and no action is specified, the packet is forwarded if it does not match any VLAN map entry.

Note You cannot combine VLAN maps or input router ACLs with port ACLs on a switch.

Guidelines for Using Router ACLs and VLAN Maps

Use these guidelines when you need to use a router ACL and a VLAN map on the same VLAN.

Because the switch hardware performs one lookup for each direction (input and output), you must merge a router ACL and a VLAN map when they are configured on the same VLAN. Merging the router ACL with the VLAN map can significantly increase the number of ACEs.

When possible, try to write the ACL so that all entries have a single action except for the final, default action. You should write the ACL using one of these two forms:

permit...permit...permit...deny ip any any

or

deny...deny...deny...permit ip any any

To define multiple permit or deny actions in an ACL, group each action type together to reduce the number of entries.

If you need to specify the full-flow mode and the ACL contains both IP ACEs and TCP/UDP/ICMP ACEs with Layer 4 information, put the Layer 4 ACEs at the end of the list. Doing this gives priority to the filtering of traffic based on IP addresses.

Examples of Router ACLs and VLAN Maps Applied to VLANs

These examples show how router ACLs and VLAN maps are applied on a VLAN to control the access of switched, bridged, routed, and multicast packets. Although the following illustrations show packets being forwarded to their destination, each time a packet crosses a line indicating a VLAN map or an ACL, the packet could be dropped rather than forwarded.

ACLs and Switched Packets

Figure 35-5 shows how an ACL processes packets that are switched within a VLAN. Packets switched within the VLAN are not processed by router ACLs.

Figure 35-5 Applying ACLs on Switched Packets

ACLs and Routed Packets

Figure 35-6 shows how ACLs are applied on routed packets. For routed packets, the ACLs are applied in this order:

1. VLAN map for input VLAN

2. Input router ACL

3. Output router ACL

4. VLAN map for output VLAN

Figure 35-6 Applying ACLs on Routed Packets

Configuring PACLs

This section describes how to configure PACLs, which are used to control filtering on Layer 2 interfaces. PACLs can filter traffic to or from Layer 2 interfaces based on Layer 3 information, Layer 4 head information or non-IP Layer 2 information.

•The number of ACLs and ACEs that can be configured as part of a PACL are bounded by the hardware resources on the switch. Those hardware resources are shared by various ACL features (for example, RACL, VACL) that are configured on the system. If there are insufficient hardware resources to program PACL in hardware, the actions for input and output PACLs differ:

–For input PACLs, some packets are sent to CPU for software forwarding.

–For output PACLs, the PACL is disabled on the port.

•These restrictions pertain to output PACLs only:

–If there are insufficient hardware resources to program the PACL, the output PACL is not applied to the port, and you receive a warning message.

–If an output PACL is configured on a Layer 2 port, then neither a VACL nor a Router ACL can be configured on the VLANs to which the Layer 2 port belongs.

If any VACL or Router ACL is configured on the VLANs to which the Layer 2 port belongs, the output PACL cannot be configured on the Layer 2 port. That is, PACLs and VLAN-based ACLs (VACL and Router ACL) are mutually exclusive on Layer 2 ports.

•The input IP ACL logging option is supported, although logging is not supported for output IP ACLs, and MAC ACLs.

•The access group mode can change the way PACLs interact with other ACLs. To maintain consistent behavior across Cisco platforms, use the default access group mode.

Configuring IP and MAC ACLs on a Layer 2 Interface

Only IP or MAC ACLs can be applied to Layer 2 physical interfaces. Standard (numbered, named) and Extended (numbered, named) IP ACLs, and Extended Named MAC ACLs are also supported.

Applies numbered or named ACL to the Layer 2 interface. The NO prefix deletes the IP or MAC ACL from the Layer 2 interface.

Step 4

Switch(config)#show
running-config

Displays the access list configuration.

The following example shows how to configure the Extended Named IP ACL simple-ip-acl to permit all TCP traffic and implicitly deny all other IP traffic:

Switch(config)# ip access-list extended simple-ip-acl

Switch(config-ext-nacl)# permit tcp any any

Switch(config-ext-nacl)# end

The following example shows how to configure the Extended Named MACL simple-mac-acl to permit source host 000.000.011 to any destination host:

Switch(config)# mac access-list extended simple-mac-acl

Switch(config-ext-macl)# permit host 000.000.011 any

Switch(config-ext-macl)# end

Using PACL with Access-Group Mode

You can use the access group mode to change the way PACLs interact with other ACLs. For example, if a Layer 2 interface belongs to VLAN100, VACL (VLAN filter) V1 is applied on VLAN100, and PACL P1 is applied on the Layer 2 interface. In this situation, you must specify how P1 and V1 impact the traffic with the Layer 2 interface on VLAN100. In a per-interface fashion, the access-group mode command can be used to specify one of the desired behaviors that are defined below.

The following modes are defined:

•prefer port mode—If PACL is configured on a Layer 2 interface, then PACL takes effect and overwrites the effect of other ACLs (Router ACL and VACL). If no PACL feature is configured on the Layer 2 interface, other features applicable to the interface are merged and applied on the interface. This is the default access group mode.

•prefer vlan mode—VLAN-based ACL features take effect on the port provided they have been applied on the port and no PACLs are in effect. If no VLAN-based ACL features are applicable to the Layer 2 interface, then the PACL feature already on the interface is applied.

•merge mode—Merges applicable ACL features before they are programmed into the hardware.

Note Because output PACLs are mutually exclusive with VACL and Router ACLs, the access group mode does not change the behavior of output traffic filtering.

Configuring Access-group Mode on Layer 2 Interface

To configure an access mode on a Layer 2 interface, perform this task:

Displaying an ACL Configuration on a Layer 2 Interface

To display information about an ACL configuration on Layer 2 interfaces, perform one of these tasks:

Command

Purpose

Switch# show ip interface [interface-name]

Shows the IP access group configuration on the interface.

Switch# show mac access-group interface
[interface-name]

Shows the MAC access group configuration on the interface.

Switch# show access-group mode interface
[interface-name]

Shows the access group mode configuration on the interface.

This example shows that the IP access group simple-ip-acl is configured on the inbound direction of interface fa6/1:

Switch# show ip interface fast 6/1

FastEthernet6/1 is up, line protocol is up

Inbound access list is simple-ip-acl

Outgoing access list is not set

This example shows that MAC access group simple-mac-acl is configured on the inbound direction of interface fa6/1:

Switch# show mac access-group interface fast 6/1

Interface FastEthernet6/1:

Inbound access-list is simple-mac-acl

Outbound access-list is not set

This example shows that access group merge is configured on interface fa6/1:

Switch# show access-group mode interface fast 6/1

Interface FastEthernet6/1:

Access group mode is: merge

Using PACL with VLAN Maps and Router ACLs

For output PACLs, there is no interaction with VACL or output Router ACLs. (See the restrictions listed in the "PACL Configuration Guidelines" section.) For input PACLs, however, the interaction with Router ACLs and VACLs depends on the interface access group mode as shown in Table 35-1.

Table 35-1 Interaction Between PACLs, VACLs and Router ACLs

ACL Type(s)

Input PACL

prefer port mode

prefer vlan mode

merge mode

1. Input Router ACL

PACL applied

Input Router ACL applied

PACL, Input Router ACL (merged) applied in order (ingress)

2. VACL

PACL applied

VACL applied

PACL, VACL (merged) applied in order (ingress)

3. VACL + Input Router ACL

PACL applied

VACL + Input Router ACL applied

PACL, VACL, Input Router ACL (merged) applied in order (ingress)

Each ACL Type listed in Table 35-1 is synonymous with a different scenario, as explained in the following discussion.

Scenario 1: Host A is connected to an interface in VLAN 20, which has an SVI configured. The interface has input PACL configured, and the SVI has input Router ACL configured as shown in Figure 35-7:

Figure 35-7 Scenario 1: PACL Interaction with an Input Router ACL

If the interface access group mode is prefer port, then only the input PACL is applied on the ingress traffic from Host A. If the mode is prefer vlan, then only the input Router ACL is applied to ingress traffic from Host A that requires routing. If the mode is merge, then the input PACL is first applied to the ingress traffic from Host A, and the input Router ACL is applied on the traffic that requires routing.

Scenario 2: Host A is connected to an interface in VLAN 10, which has a VACL (VLAN Map) configured and an input PACL configured as shown in Figure 35-8:

Figure 35-8 Scenario 2: PACL Interaction with a VACL

If the interface access group mode is prefer port, then only the input PACL is applied on the ingress traffic from Host A. If the mode is prefer vlan, then only the VACL is applied to the ingress traffic from Host A. If the mode is merge, the input PACL is first applied to the ingress traffic from Host A, and the VACL is applied on the traffic.

Scenario 3: Host A is connected to an interface in VLAN 10, which has a VACL and an SVI configured. The SVI has an input Router ACL configured and the interface has an input PACL configured, as shown in Figure 35-9:

Figure 35-9 Scenario 3: VACL and Input Router ACL

If the interface access group mode is prefer port, then only the input PACL is applied on the ingress traffic from Host A. If the mode is prefer vlan, then the merged results of the VACL and the input Router ACL are applied to the ingress traffic from Host A. If the mode is merge, the input PACL is first applied to the ingress traffic from Host A, the VACL is applied on the traffic and finally, and the input Router ACL is applied to the traffic that needs routing. (that is, the merged results of the input PACL, VACL, and input Router ACL are applied to the traffic).